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LA OROGENESIS DE GRENVILLE EN LAS SIERRAS PAMPEANAS OCCIDENTALES: LA SIERRA DE PIE DE PALO Y SU INTEGRACION AL SUPERCONTINENTE PROTEROZOICO Vidor A. Ramos (1), Graciela Vujovich (2), Suzanne Mahlburg Kay (2) y Michael McDonough (3)

IJ Ulliversid'ld ric Huenos Aires 2! /N STOC, Cornell University, Estarlos Unidos J) Cell/ogi,:a / Surwy of GUlilila, Ca lgary . d,\.' il l j .. I . 1

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ABSTRACT. The Sierra de Pie de Palo, western Sierras Pampeanas of the province of San Juan, is a critical area to understand the Proterozoic h" tory and the palwgeographyof the Late Precambrian supercontinent. l\:c'" geochemica l data of some representative amphibolites, confirm Ih"ir affin iti es with island arc tholeiites, in a similar way than other mafic rocks of \\'es tcrn Sie rra s Pampeanas. The ages recent! y obtained i,'r the magmatic, metamorphic, and volcani c rocks indicateaGrenville J~e for th is association, ranging from 1.1 to 1.0 Ca. The western Sierras l'd l11pca nas has be'~11 proposed as the continental margin of Western Condwanaland. nH~rdore thi s area is critical to test the different hypothesis r~ullillg from the SWEAT and later proposals. Afler JnJ I)'I.ing several pre-existing models it is concluded that if North ,\Ill,'rica and SOllth America h ave been toge lh er, the formation of the Cr~nvi ll c orogen was th e most s lIitable time to place next to each other b,)th continen ts. In that model Precordillera was detached from I Jllr,' nlia about 600 m .y. ago,and collided aga in st WestGondwanaland JI J 1,ller time (ca. ·150 Ma).

INTRODUCCION EI objctivo del presente trabajo es analizar la evolucion It'donica del hJsamento de la Sierra de Pie de Palo, sabre la base de nuevas observaciones geologicas, geoqufmicas y g,'()cronoI 6gicas para integrarla dentro del marco regional de L'\'oluei6n te(tonica del supercontinente proterozoico. Sobre ",t